ddd079b54f
`GVolumeGrid` and `VolumeGrid<T>` are basically pointer wrappers. Assigning a nullptr is possible and allowed by code, but node socket code doesn't currently check if a grid pointer is null before accessing it. Disallow null grid pointers in socket values. Asserts are added for this purpose. The Points-to-SDF node checks the grid value before writing to output. Pull Request: https://projects.blender.org/blender/blender/pulls/122996